feat(PocomathInstance): Add bounded template parameters

This feature helps specify the return type of implementations where
  the return type depends on the exact subtype that the implementation
  was called with, such as negate.

test/_pocomath.mjs

@@ -27,7 +27,7 @@ describe('The default full pocomath instance "math"', () => {
 
    it('can subtract numbers', () => {
       assert.strictEqual(math.subtract(12, 5), 7)
-      //assert.strictEqual(math.subtract(3n, 1.5), 1.5)
+      assert.throws(() => math.subtract(3n, 1.5), 'TypeError')
    })
 
    it('can add numbers', () => {